how to create a application level variable

Anon

I want to define a variable in one php file and use it in another pho file. How do I do that? Actally I want to this variable shared in the whole application.

Anon

you can a) use a database or text file.

or easier still post the variable from page to page in the url or as a hidden form field,

if you set a var $var="hello" and then move on to page2.htm you make the link so <a href="page2.htm?var=hello">etc</a>

or use a variable there <a href="page2.htm?var=<? echo $var;?>">etc</a>

on page2.htm $var is ready to use.

Anon

use the include() function

write a small php file called something like config.php.

<?
$my_var=2;
?>

then add this to your other scripts, somewhere at the top:

include("config.php");

your new variable should be available after this line.

Anon

vincent - that just makes $my_var a constant not a variable.

Anon

Yes and no,
it does give the same value to every script that calls it, but
after being called it can be changed by the script, so it's not a true constant.

It's pretty difficult to have a true application-wide variable, as many scripts may run at the same time, changing the variable at the same time.

Handing the variable down using the URL makes the variable available only to that particular user-session, not to the rest of the app.

I guess the final way of doing it depends on what the variable is used for.

Anon

The problem here is:
the data will be generated dynamically and only need to be generated once, after that we need to fetch it on every php page without reading from file or db. Also this data is common to all request sending to the website.

Any ideas?

Anon

A true application-wide variable that you can set from s php script does not exist as far as I know.

But the functionality is pretty much the same as using an include file.

It takes near zero cpu to do, and does exactly what you want.

I use an include() to read the system config for my project.
It contains information about databasenames, page layout etc.
Everything I want to use for all my scripts in the project.
Thus, if I want to change databases, I only change the content of the include file, and every script using that file will automatically use the right data.

Try it, you might like it.

Anon

As I said before - a value from a static include file is not a variable - it is a constant, when you call it and change its value it is then a variable but only in the scope of that document, unless that document writes the new value back to the include file.

I am not sure why Jennys app can not check a db or flatfile for the value and then change it - the overhead for opening and closing a small text file is very small.

However if that is the case passing the variable around via the url as shown above or via posted form variables is pretty easy.

I can think of reasons not to use the query string , not so many for posting data, and depending on how much info you need to store as a pseudo-global' variable, there is always the option of using cookies.

Anon

Firepages: read jenny's message.

The data will be generated dynamically and only need to be generated once, after that we need to fetch it on every php page without reading from file or db. Also this data is common to all request sending to the website.

If this doesn't spell CONSTANT then I don't know what does.

Anon

and I totally agree - however the original question or at least title of the post was how to create an application wide 'variable'!

After Jennys last post it looks more like she is looking for a constant, and an include() for that is fine - great even - I use them every day!!

I was commenting on variables.

Anon

So we were both right! :-)

This just proves that when people ask a question they should tell as much about their problem as they can so that us geniuses don't get confused.

Anon

O.K. I guess I didn't make my question clear enough. My fault...

The reason I initially posted message asking application level variable is I thought there is a similar type of variable as session variables, you can register it and use it whenever and wherever you want and it is application wide, Also you can check it whether it is registered.
I tried contant at that time and it turns out that each file seems to have to include the file that generates and defines the constant if I want to use it.
I don't want to generate the constant every time I want to use it since generate the constant need to parse some other file and doing extra things. This is also the reason I am saying that the variable I need is only need to be generated once.

Right now I am thinking generate the contant file dynamically( if it exist, don't need to generate,otherwise go through the logic and generate it) and include it.

Any thoughts?

Hopefully, I explain my question clearly this time. If not, let me know

-- jenny

Anon

O.K. I guess I didn't make my question clear enough. My fault...

Right now I am thinking generate the contant file dynamically( if it exist, don't need to generate,otherwise go through the logic and generate it) and include it.

Any thoughts?

Hopefully, I explain my question clearly this time. If not, let me know

-- jenny

erebos

Hello,

Ive made something that works like that
http://www.phpbuilder.com/snippet/detail.php?type=snippet&id=259

its still underdevelopment..., but it gives your application variables.

Anon

i d like to know how to do that with a real variable or an array.
see, i can not pass on too many variables within an URL for i-mode phones (only 100 characters i think), now i wonder how i ll store the received variables between the many i-mode pages (it takes about 5 imode pages to get the whole data).

any idea?

and concerning the "constant" problem. i think there might be something about this topic within SSI - and access the constant by PHP... but i never tried this...

techsoldaten

Hi, I use PHP infrequently compared to ASP or Cold Fusion exactly because of the lack of application scope. For that matter, also because there is no request scope - a variable that exists for the time it takes to build a page.

The main product I support stores arrays of data in cold Fusion application variables and does all of it's queries against those arrays. There are fewer round trips to the server and FAR less overhead because of the fact these variables are not being built each time a page loads. We have a trigger set on the database to refresh them every time important data is modified (i.e. a new business unit added, a new report becomes available, etc.)

We also use request variables all over the place. Not only do they cut down on total memory size in that they disappear once the page has loaded, but they are also extremely important in some types of conditional processing.

Without trying to sound too critical, I really have to wonder why something as critical as an application scope could be overlooked for so long? I see a lot of suggested work arounds that just seem to ignore the benefits of what such a scope would bring; prehaps PHP is not really ready for the big time yet at all?

Mike Haggerty
Senior Manager, Web Information Technology
Nucleus Technologies, Inc.

Anon

An application wide global variable is no more (in ASP for instance) than a textfile with variables contained in it that can be accessed by all scripts running for all concurrent users.

PHP does not put the same importance on application wide variables as other languages simply because there are so many other ways to achieve the desired results, a DB or flatfile can hold application wide variables and be included() or altered at any time by any script for any user.

Tha majority of pages on any given site that actually need this information is low, critical where needed , but not needed that often, having this information loaded into , or hanging around in memory when not needed is a waste of time and resources, call it when you actually need it.

Thats part of why PHP is so much faster than most of the other runners, like the need for a unified DB API (which is here anyway with the dbx functions) this is an argument that does not hold water. IMO 🙂

[deleted]

Took the words right out of my mouth FP. :-)

techsoldaten

An application variable in Cold Fusion is kept exclusively in RAM. I haven't looked into this is ASP, so it may be kept in a text file, but it is in memory in Cold Fusion.

Besides all of the documentation on Allaire's Web site about where application variables actually reside, I can prove this point to you by loading 5 megs of data into the application scope and watching the memory allocation grow by 5 megs.

Application variables are specific to applications as well. For instance, if I have two copies of the same app running into two subdirectories on the same server (for different comapnies, perhaps) the applciation variables for each are available only for that application.

In terms of performance, this is a major advantage for many of the apps I have worked on. The need for a unified DB API is greatly reduced, in that I have entire tables in memory as arrays that can be accessed far more quickly by their position than by going to the DB. Queries run much faster, pages take less time to generate, and the load on the server never reaches a critical stage.

The other variable scope that is not present in PHP that is very useful is the client scope, which probably sounds a lot like session but persists between sessions. These variables are stored either in the registry or a DB, but they are available in RAM after a user returns to the site. Major time saver.

Maybe I am the only one to think this, but I would really like to see this kind of functionality in PHP.